DiscountBill. Suppose a class GroceryBill keeps track of a list of items being purchased at a market:

Grocery bills interact with Item objects, each of which has the public methods that follow. A candy bar item might cost 1.35 with a discount of 0.25 for preferred customers, meaning that preferred customers get it for 1.10. (Some items will have no discount, 0.0.) Currently the preceding classes do not consider discounts. Every item in a bill is charged full price, and item discounts are ignored.

Define a class DiscountBill that extends GroceryBill to compute discounts for preferred customers. Its constructor accepts a parameter for whether the customer should get the discount. Your class should also adjust the total reported for preferred customers. For example, if the total would have been $80 but a preferred customer is getting $20 in discounts, then getTotal should report the total as $60 for that customer. Also keep track of the number of items on which a customer is getting a nonzero discount and the sum of these discounts, both as a total amount and as a percentage of the original bill. Include the extra methods that follow, which allow a client to ask about the discount. Return 0.0 if the customer is not a preferred customer or if no items were discounted.